In recent years immune sera have been raised which frequently recognize nuclear antigens with limited cellular distributions. Immunogen prepared from isolated peripheral blood human granulocyte chromatin was used to produce antisera specific for human neutrophilic granulocyte nuclear antigens. We propose the following areas for investigation of these unusually specific nuclear antigen: (1) The antigens will be isolated and characterized. Their localization within the chromatin structure will be determined using recently developed enzyme digestion and fractionation schemes. This information combined with the molecular characteristics will be used to assign functional roles. (2) Immunocytochemical staining of normal and pathologic bone marrow aspirates and peripheral blood specimens show that all late stage myeloid cell nuclei react. To further elucidate a possible role in cellular differentiation, the antigens will be studied in cultures of myeloid leukemic cells, both induced and non-induced to differentiate. In another approach, antigens will be studied in cultured cells as well as specimens of myeloid leukemia separated into early and late stages by density gradient centrifugation. (3) The normal myeloid chromatin antigens were found in chromatin isolated from a specimen of CML. Immunocytochemical staining of CML and AML showed nearly every cell nucleus positively reacting. However, chromatin isolated from a cell culture of acute promyelocytic leukemia showed only one of the three normal myeloid chromatin antigens by immunodiffusion reaction. No cross reacting antigens have been found in any other leukemias. The usefulness of the antisera in differentiating types of leukemias or in monitoring therapy will be determined by comparing the immunocyto-chemical reaction with the results of current diagnostic methods. (4) New antisera will be developed to chromatin antigens of other hematopoietic cell types, both normal and leukemic.